L 151 J 



XX. Intelligence and Miscellaneous Articles. 



VISIBLE REPRESENTATION OF THE EQUIPOTENTIAL LINES IN 

 PLATES TRAVERSED BY CURRENTS ; EXPLANATION OF HALL'S 



phenomenon. BY E. lommel. (Preliminary Notice.) 



SIMPLE consideration shows that the equipotential lines at right 

 angles to the lines of flow in a plate are at the same time the 

 magnetic lines of force belonging to the flow. If iron filings are 

 strewed on the plate with a sufficiently strong current, they 

 arrange themselves to form a beautiful image of the equipotential 

 lines. 



If the plate is brought into a magnetic field these magnetic 

 lines of force alter their position, and therefore also the lines of 

 force which necessarily are at right angles to them. In this lies 

 the simple explanation of Hall's phenomenon. — Wiedemann's 

 Annalen,TXo. 12, 1892. 



ON THE ACTION OF LIGHT UPON ELECTRICAL DISCHARGES IN 



VARIOUS GASES. BY F. BREISSIG. 

 As source of light the author used a gas-flame. As he had the 

 intention of determining the influence of the visible rays in 

 electrical discharges, he tried to find a gas in which this action is 

 as great as possible, but he came to the conclusion that the 

 difference between various gases in this respect is too small to 

 lead to the preference of any one in particular. 



M. Breissig uses Hallwachs' form of the luminous discharge with 

 a somewhat different arrangement. Opposite the source of light 

 is placed an amalgamated zinc plate, and in front of it a wire 

 gauze, also amalgamated, of galvanized iron, both being insulated. 

 The zinc plate was kept at constant potential by a Daniell's batter v 

 of 80 elements, while the wire gauze was connected with one 

 quadrant pair of an electrometer. The potential was measured of 

 the quantity of electricity passing from the zinc plate to the wire 

 gauze owing to illumination. 



A decrease of sensitiveness of the plate with the duration of 

 the illumination was observed, as Hallwachs and Bighi had also 

 observed for other sources of light; moreover, an increase was 

 observed in all the gases investigated as the pressure diminished. 

 In opposition to the observations of others, the author found a 

 feebler discharge in carbonic acid than in air ; the deflexions are 

 reduced to about one half : this phenomenon is due to the fact 

 that in his experiments the rays of a spectral region are used 

 differing from that of other observers, and the action of the 

 various parts of the spectrum on many gases maybe different. 

 With cool gas a feebler action is observed if the gas has already 

 been illuminated. 



The discharges in some vapours were stronger than in all the 

 gases examined, especially in air half saturated with alcohol vapour. 

 The following table gives in round numbers the results observed 

 by the author. 



